How does Teamcity clean .old folder? Looks like it does not delete last build results

We have builds that uses more than a half of free disk space on agent (60gb of 100). And build is failing due to lack of disk space. We configured "Free disk space" requirement on all builds. But seems that when we have two serial greedy builds the results of finished one from .old directory not removed by agent software.

Here is an example. Greedy build has finished, new one is working for several minutes. It reported in log that can not free enough disk space and started working. Here is how disk usage looks:

$ du -h -d1 buildAgent/work/
60G buildAgent/work//.old
10G buildAgent/work//6d6a584026202b3d
...

And thats how in look inside .old:

$ du -h -d1 buildAgent/work/.old/
60G buildAgent/work/.old//6d6a584026202b3d_7
0B buildAgent/work/.old//6d6a584026202b3d_8
0B buildAgent/work/.old//6d6a584026202b3d_9

Is it a bug or thats how it should be?